1. Field Of The Invention
The present invention relates to orthopedic surgical instruments and prosthetic devices and more particularly relates to an improved instrument for cutting the distal femur of a patient to receive a unicondylar prosthetic component and such a unicondylar prosthesis. Even more particularly, the present invention relates to improved surgical instrumentation for shaping the distal femur of a patient to receive a unicondylar prosthetic component wherein a cutting guide body has a pair of cylindrically shaped, overlapping openings which are angled with respect to each other and wherein a surgeon can make sequential dished cuts in the patient's distal femur by placing a rotary reamer in one of the angled openings and then in the other of the angled openings to produce an overlapping, oval shaped convex surface on the diseased condylar portion of the distal femur. The prosthesis has a distal surface which is shaped to fit the prepared bone surface.
2. General Background
Various types of instruments and methods have been developed to enable a surgeon to affix a distal femoral knee prosthesis to the human femur. The femoral prosthesis may be a bi-condylar prosthesis as used in total knee arthroplasty, or it may be a unicondylar prosthesis where only one condyle of the femur is affected and thus in need of replacement.
The purpose for affixing such a prosthesis is to restore the patient's ability to walk after disease or other traumatic causes affecting the knee which have impaired that ability. It is important that the prosthesis be attached to the femur in such a manner that it will approximate as closely as possible, the natural femoral condyle(s). Therefore, the initial shaping of the distal end of the femur is critically important.
A British patent No. 1,534,263 issued to Goodfellow utilizes a concave cutting tool to prepare the distal end of one condyle, the prosthesis having a rear surface which has a portion curved in three dimensions and another portion with an axis of rotation parallel to the axis of the femoral shaft.
U.S. Pat. No. 4,719,908 to Averill et al utilizes a contouring guide for guiding a burr assembly along a condyle for preparing the surface to receive an unicondylar prosthesis. A prosthetic implant is then implanted which has an inner surface that matches the curved contour formed as a result of the configuration of the guide.
Some methods and devices for cutting the distal femur use the central longitudinal axis of the femur (i.e. intramedullary canal) as an aid in shaping the distal femoral surface. These prior art methods and devices insert an alignment rod into the intramedullary canal of the femur. The alignment rod protrudes a substantial distance from the femur after it is inserted. Cutting guides and drill templates are then positioned on or around the rod in an abutting contact with the condyles of the femur in order that the surgeon can accurately resect the condyles and/or drill holes in them. Once the distal femur is properly shaped for receiving the femoral prosthesis, the physician may attach it to the distal femur.
U.S. Pat. No. 4,474,177 issued to Whiteside shows a device that uses the intramedullary canal of the femur for shaping and drilling the femoral condyles (see for examples FIGS. 8-23 of Whiteside). The Whiteside device could be used in a unicondylar replacement operation or in a total knee replacement.
Other patents have issued which describe methods for shaping a distal femoral surface.
The following listed patents describe devices for shaping the distal femoral condyles and without using an intramedullary stabilizing spike:
______________________________________ U.S. Pat. No. Assignee/Patentee ______________________________________ 4,926,847 Johnson & Johnson 4,892,093 Osteonics Corp 4,773,407 T. D. Peterson 4,721,104 Dow Corning Wright 4,718,413 Orthomet Inc. 4,574,794 Queen's Univ. Kingston 4,566,448 W. L. Rohr 4,524,766 T. D. Peterson 4,502,483 Dow Corning Corp 4,457,307 W. T. Stillwell 4,349,018 G. R. Chambers 327387 EPO J. W. Goodfellow ______________________________________
Other devices are used for shaping the femoral condyles which use an intramedullary spike:
______________________________________ U.S. Pat. No. Assignee/Patentee ______________________________________ 4,935,023 Dow Corning Wright 4,907,578 T. D. Peterson 4,825,857 Howmedica 4,759,350 H. K. Dunn 4,738,254 Biomed Eng. Trust 4,738,253 Biomed Eng. Trust 4,722,330 Dow Corning Wright 4,703,751 K. P. Pohl 4,653,488 Howmedica 4,646,729 Howmedica 4,567,885 G. W. Androphy 4,487,203 G. W. Androphy 4,474,177 Wright Manf. Co. ______________________________________
U.S. Pat. Nos. 4,787,383; 4,567,886; and 4,211,228 are patents directed to devices for shaping either the femur condyles or the tibial surface.
U.S. Pat. Nos. 4,959,066 and 4,621,630 illustrate devices for operating on the proximal end of the femur.